The full scale prototype of the cylindrical-GEM detector as inner tracker in KLOE2

We are developing a low mass, fully cylindrical and dead-zone-free GEM detector as inner tracker for the KLOE experiment upgrade at the DAFNE Phi-factory. The proposed detector will play a crucial role in the study of the K_S rare decays and in the measurement of the neutral kaon interferometry. The main physics requirements are: a good detector spatial resolutions, (sigma_rPhi sime 200 mum and sigma_Z sime 500 mum) and a very low material budget inside the active area (1.5% of X₀ for the whole sub-detector). The inner tracker will be composed by live layers of cylindrical triple-GEM detectors (C-GEM), covering the space from the beam pipe to the inner cylinder of the KLOE main drift chamber (from 150 mm to 250 mm radius). Each C-GEM is realized inserting one into the other the required live cylindrical structures made of thin (50 mum) polyimide foils: the cathode, the three GEMs and the anode readout. The final result is a very light detector: only 0.2% of X₀ per tracking layer inside the active area. After the successful construction and test of a small size prototype (90 mm diameter, 250 mm length), a full scale prototype (300 mm diameter, 352 mm length) of the first layer of the inner tracker has been designed in all details, namely mechanics, readout and front-end electronics, exploiting many of the technical solutions we studied and implemented for the planar GEMs of the LHCb experiment, adapted for the cylindrical geometry. We report about the design, the construction and some preliminary test of such a large prototype that opens the way for a new and competitive category of ultra-light micro-pattern gas vertex detectors.